The invention relates to a fuel injection system for mixture compressing, externally ignited internal combustion engines employing continuous fuel injection into the induction tube. The induction tube includes a converging section and, immediately behind it as seen in the direction of air flow, a diverging section. Located in this part of the induction tube is a throttling, element which may be arbitrarily moved in its axial direction and which is composed of substantially two conical portions with the bases of the cones adjacent to each other. The cones have different apex angles and the throttle element cooperates with the diverging section of the induction tube to form a restricted annular air flow passage and, downstream thereof, to form a diffuser having a small divergent angle. Fuel is injected at the narrowest part of the air flow passage. That conical portion of the throttle element which converges in a direction opposite to the air flow direction has a larger apex angle than the other conical portion of the throttle element. The system includes means to equalize the pressures acting on the throttle element.
Fuel injection systems of this type serve the purpose of automatically creating a favorable fuel-air mixture for all operational conditions of the internal combustion engine so as to make possible complete combustion of the fuel and thus to avoid the generation of toxic exhaust gas constituents while maintaining the highest possible performance or the lowest possible fuel consumption. This requires that the fuel quantity be metered out precisely according to the requirements of each operational state of the internal combustion engine.
In engines employing carburetors it is known to achieve adequate fuel vaporization in that the fuel, which is introduced into the aspirated air upstream of the throttle valve, experiences the sonic velocity prevailing at the throttle valve. Behind the throttle valve, however, two separate streams of fuel-air mixtures having differing concentrations are formed and this leads to an asymmetric distribution of the fuel within the mixture. When the engine is accelerated or when it is operating under load, this mixture is even less favorable because the air passing the throttle valve does not reach sonic velocity, thus permitting unvaporized fuel to reach the engine cylinders. Such mixtures result in high concentrations of uncombusted hydrocarbons and the presence of carbon monoxide and nitrogen oxides in the exhaust gas.
In known fuel injection systems it is therefore proposed to provide a throttling element in a venturi-like region of the induction tube so constructed that sonic velocity always prevails at the minimum cross section formed by the throttling element and the venturi-like member of the induction tube, thus permitting an optimized preparation of the fuel for combustion. The need to prevent the presence of toxic components in the exhaust gas of the internal combustion engine makes it necessary to maintain, if possible, a stoichiometric fuel-air ratio by regulation.